Vulcanization of ethylene-propylene-diene terpolymers

ABSTRACT

Ethylene-propylene-diene terpolymer elastomer compositions having improved vulcanization properties containing auxiliary vulcanization accelerators selected from mono and dihydrazide derivatives of monobasic and dibasic organic acids containing C2 to C40 carbon atoms and having alkyl, aryl, alkenyl and cyclic structures.

Unite States Patent [191 Boyer et al.

[ 1 Feb. 27, 1973 1 VULCANIZATION OF ETHYLENE- PROPYLENE-DIENE TERPOLYMERS [75] Inventors: Jackson S. Boyer, Wilmington, Del; Richard D. Cassar, West Chester, Pa. [73] Assignee: Sun Oil Company, Philadelphia, Pa.

[22] Filed: June 23, 1970 [21] Appl. No.: 49,177

[52] US. Cl. ..260/79.5 B, 260/557 H, 260/558 H, 260/561 H, 260/785, 260/793, 260/794 [51] Int. Cl. ..C08t 27/07, C08d 9/00 [58] Field of Search .....260/79.5 B, 785, 795, 557 H, 260/558 H, 561 H, 775

[56] References Cited UNITED STATES PATENTS 2,851,507 9/1958 St. John, Jr ..260/780 3,308,103 3/1967 Coran ..260/79.5

3,400,106 9/1968 Morita ..260/79.5

OTHER PUBLICATIONS Nischk, (1., Chem. Abst., 54, 20, 340 h.

Primary Examiner-James A. Seidleck Assistant Examiner-C. A. Henderson, Jr. Attorney-George L. Church, Donald F. Johnson and Wilmer E. McCorquodale, Jr.

[5 7 ABSTRACT 14 Claims, No Drawings VULCANIZATION OF ETHYLENE-PROPYLENE- DIENE TERPOLYMERS CROSS REFERENCES TO RELATED APPLICATIONS The present application is related to copending application Ser. No. 49,176 by Anne R. Donnell which discloses as new compositions of matter the mono and dihydrazide derivatives of certain methylated muconic acids which are effective in the improvement of viscosity stability of synthetic elastomers. This application is also related to our copending application Ser. No. 49,179 which discloses as new compositions of matter mono and dihydrazides of naphthalene dicarboxylic acids which have been found suitable for use in viscosity stability improvement of synthetic elastomer compositions. This application is also related to our copending application Ser. No. 49,178 which discloses synthetic elastomers having improved resistance to viscosity breakdown when extended with petroleum hydrocarbon oils and containing dihydrazides of monobasic and dibasic organic acids containing C to C carbon atoms. All of these corelated applications are of common ownership and have been filed of even date herewith.

BACKGROUND OF THE INVENTION The problems related to the vulcanization of elastomers are many and complex. U.S. Pat. No. 1,418,825 to Ralph B. Naylor issued June 6, 1922 discloses the use of phenylhydrazine to accelerate the vulcanization of natural rubber. U. S. Pat. No. 2,851,507 to Willerd N. St. John, Jr. et a1. issued Sept. 9, 1958 discloses the addition of mono and dihydrazides of monobasic and dibasic organic acids to natural rubber to inhibit scorch during vulcanization preparation of natural rubber. Specifically, it is generally known that vulcanization accelerators when employed in the manufacture of natural rubber products often resulted in precuring or prevulcanization of the raw natural rubber composition. This precuring or prevulcanization'is known as scorching. When premature cross-linking (scorching) occurred in the rubber being processed, the step of forming the rubber into its ultimate useful shape was very difficult. Thus it was disclosed that the addition of hydrazides to a natural rubber composition delayed or inhibited scorching and thereby improved the proeessability of natural rubber. Thus St. John et a1. teaches that the addition of the dihydrazides and monohydrazides of monobasic and dibasic organic acids retards scorching of natural rubber compositions during the vulcanization process.

With the advent of synthetic polymers, it has been discovered that the vulcanization process in general and curing additives in particular must be tailored to the particular chemical make-up of each synthetic elastomer being treated. For example, the curing of styrene-butadiene polymer requires one set of processing conditions and a specific set of vulcanization agents, whereas ethylene-propylene copolymer elastomer normally cannot be easily cured under the same processing conditions and with the same vulcanization agents as those disclosed for the styrene-butadiene polymer. Thus it has been found that the art of vulcanization of synthetic elastomers is at best unpredictable and each of the elastomers must be provided for in accordance with its own requirements.

One of the most interesting recent advances in rubber technology is the development of ethylenepropylene tcrpolymcrs. This new class of elastomer polymers is comprised normally of three monomers which include ethylene, propylene and a third diene monomer (EPDM The added third monomer which is a diene provides the ethylene-propylene copolymer with the advantage of being sulfur vulcanizable. Coincidentally, with the advent of these new terpolymers is 0 the need for the development of a process to vulcanize these new terpolymer compositions to provide a synthetic elastomer of superior physical characteristics. One of the significant problems encountered in attempting to vulcanize ethylene-propylene-diene polymers (EPDM) is the slow rate of cure normally associated with these polymers. Contrary to the experience found with natural rubber, ethylenepropylene-diene polymers suffer little from scorch. To the contrary, the polymers cure so slowly that commercial manufacturing is economically questionable because of the extensive time of vulcanization.

Several of the well known vulcanization accelerators have been used with EPDM polymers. However, the use of the known vulcanization accelerators with these new elastomers has met with only limited success. A new class of auxiliary accelerators particularly suitable for use with EPDM polymers has now been discovered.

DESCRIPTION OF THE INVENTION It has now been discovered that the hydrazide derivatives of both monobasic and dibasic organic acids having from 2 to 40 carbon atoms when added to sulfur vulcanizable ethylene-propylene-diene terpolymers (EPDM) in combination with sulfur containing primary and secondary curing additives substantially accelerate the curing process.

The EPDM polymer synthetic elastomers of the present invention include copolymers of ethylene and propylene and a third unconjugated diene monomer including such polymers as ethylene-propylene-l,4-hexadiene; ethylene-propylene-dicyclopentadiene; ethylene-propylene-S-methylene-2-norbornene; ethylene-propylene- 1 ,S-cyclooctadiene; ethylenepropylene-allene and others. These terpolymers are well known standard articles of commerce. Methods of preparing the EPDM polymers included in the compositions of the present invention are disclosed in U.S. Pat. No. 2,933,480 issued Apr. 19, 1960; U.S. Pat. No.

3,000,866 issued Sept. 19, 1961; U.S. Pat. No. 3,063,973 issued Nov. 13, 1962; U.S. Pat. No. 3,093,620 issued June 11, 1963; U.S. Pat. No. 3,093,621 issued June 11, 1963; U.S. Pat. No. 3,260,708 issued July 12, 1966; U.S. Pat. No.

3,310,537 issued Mar. 21, 1967 and others.

Examples of EPDM elastomers and vulcanizing systems are disclosed in Development Products Report No. 20 on NORDEL Hydrocarbon Rubber, a technical report by E. l. duPont de Nemours and Company, Inc. (May 1963). Suitable primary and secondary accelerators for vulcanization of EPDM elastomers are also disclosed in The Vanderbuilt Rubber Handbook" ed. by George G. Winspear, R. T. Vanderbuilt Company, lnc.., N.Y., N.Y. (1968), pages -74.

Examples of sulfur containing primary accelerators normally used in vulcanization of EPDM elastomers include:

Tetramethylthiuram disulfide 3 4 Tetraethylthiruam disulfide tives of monobasic organic acids are the preferred addi- Dipentamethylenethiuram hexasulfide tives. Tetramethylthiruam monosulfide The auxiliary accelerators of the present invention Dimethylthiourea can be of the structural formula Examples of secondary sulfur containing accelerators normally used in vulcanization of EPDM elastomers include:

Benzothiazolyl disulfide z'mercaptobenzothlazole wherein Y is selected from N-oxydiethylene benzothiazole-2-sulfenamide 1O N-cyclohexyl-2-benzothiazolesulfenamide Sodium 2-mercaptobenzothizole l Zinc Z-mercaptobenzothrazole 2,2'-dithiobisbenzothiazole 2-(morpholinothio)-benzothiazole 2-benzothiazolyl l-hexamethyleniminecarbodithioate 0 Z-benzothiazolyl-thiolbenzoate J l,3-bis(2-benzothiazolylmercaptomethyl) urea 2-(2,4-dinitrophenylthio) benzothiazole S(2-benzothiazo lyl) N,N-diethyl dithiocarbamate N-cyclohexylbenzothiazole-Z-sulfenamide N-tert-butylbenzothiazole-2-sulfenamide and hydrogen, and R can be a divalent C to C hydrocarbon alkyl. Compounds wherein Y is can include the dihydrazides of dibasic acids such as:

Malonic Acid Succinic Acid A typical example of a formulation of a vulcanizable i k i fg EPDM elastomer composition comprises: f

Pimelic Acid NORDEL i070 EPDM 100.0 Parts by Weight suberfc f Zinc Oxide 5.0 Parts by Weight AZBlOlC Acid Tetramethylthiuram Monosult'ide 1.5 Parts by Weight l l Mercaptobenzothiazole 0.5 Parts by Weight Bassylic Acid Sulfur 1.5 Parts by Weight HAF Carbon Black 50.0 Parts by Weight Acld Process Oil 20.0 Parts by Weight Eicosandioic Acid Tricosandioic Acid This formulation provides an EPDM elastomer hav- Triacontanedioic Acid ing an optimum cure after approximately 22 minutes at Heptatriacontanedioic Acid 320 F. By the methods and compositions of the Tetracontanedioic Acid present invention, the time to optimum cure is substan- Compounds in which Y is hydrogen can include the tially reduced. monohydrazides of The compositions of the present invention contain a Ac tic Acid new auxiliary secondary accelerator which when added propionic Acid to the presently used vulcanization formulas for curing Butyric Acid EPDM elastomer provides a cured elastomer composi- Valerie Acid tions in a substantially reduced amount of time. Caproic Acid The class of compounds suitable as auxiliary ac- Enamhic Acid celerators for vulcanization of EPDM polymers in ac- Caprylic Acid cordance with the methods and compositlons of the pelargonic Acid present invention can be defined as mono and dihydra- Capri: Acid zides of monobasic and dibasic organic acids having the general structural formula 44-dimethyloctanoic Acid n-Stearic Acid 0 Cerotic Acid n-triacontanic Acid Hexatriacontanic Acid n-Tetracontanic Acid Eicosanedioic Acid 0 n-tetracontanedioic Acid l u, Each of the monobasic and dibasic organic acid hydrazides disclosed above and hereafter can be obd hydrogen, R i a di l (3 to c h d b 6o tained by reacting a solution of the respective acid with di L T R group i thg above di l d Structural a stoichiometric quantity of hydrazine in solution at a formula can be a C to C divalent hydrocarbon radical mperature in the range of 50 to 210 F. Thereafter wherein Y is selected from which can be aryl, alkyl, alkenyl and cyclic in structure. the desired hydrazide derivative can be recovered by Although both the monohydrazides and dihydrazides of procedures such as solvent extraction or recrystallizathe above disclosed organic acids are effective in imtion, methods well known to those skilled in the art.

proving the vulcanization of EPDM synthetic The preferred method of preparing hydrazides utilizes elastomeric compositions, the monohydrazide derivathe mono and diester of the acid as a starting material.

As an illustration of one method of preparing the dihydrazide derivative of a dibasic acid, a 400 milliliter solution of methanol containing 35 grams of the dimethyl ester of succinic acid dissolved therein was admixed with 200 milliliters of methanol containing 35 grams of dissolved hydrazine hydrate. The solution was agitated for 1 hour at a temperature of 104 F. and thereafter permitted to cool to room temperature. After 96 hours a white crystalline precipitate was recovered from solution and identified to be the dihydrazide of succinic acid. The mono and dihydrazide of other dibasic acids as well as the monohydrazides of monobasic acids can be prepared in a manner similar to that disclosed hereinabove for succinic acid.

Another class of compounds suitable as auxiliary accelerators for vulcanization of EPDM elastomers in accordance with the methods and compositions of the present invention can be defined as having the general structural formula wherein Y is selected from acid hydrazide the dihydrazide compounds suitable for use in the present invention can include:

1,2-cyclopropane dicarboxylic acid dihydrazide 1,4-cyclohexane dicarboxylic acid dihydrazide 1,5-cyclooctane dicarboxylic acid dihydrazide l,7-octadecahydrochrysene dicarboxylic acid dihydrazide '1,4-tetrahydronaphthlene dicarboxylic acid dihydrazide Bicyclopentyl 3,3'-[bis(4-cyclohexyl-dicarboxylic acid dihydrazide)] 1,3-cyclopentyl dicarboxylic acid dihydrazide 1,4-cyclohexane dicarboxylic acid dihydrazide Hexacosane a di( 4-cyclohexane dicarboxylic acid dihydrazide) Bicyclopenty1-3,3-dicyc1ohexyl-4,4-dicarboxylic acid dihydrazide Sexicyclopentyl-3,""-dicarboxylic acid dihydrazide Another class of hydrazide compounds suitable for use as auxiliary accelerators in vulcanizing EPDM elastomer compositions can be defined as having the general structural formula wherein Y can be or hydrogen and R is a C to C divalent alkenyl hydrocarbon radical. In the instance wherein Y is hydrogen, the monohydrazides suitable for use in the present invention include:

Acrylic acid hydrazide Sorbic acid hydrazide 4-pentenoic acid hydrazide A -decylenic acid hydrazide Oleic acid hydrazide Gadoleic acid hydrazide A -triacontenic acid hydrazide A -tetraconteric acid hydrazide 1n the instance wherein Y is- O NIINHz dihydrazide compounds suitable for use in the instant invention include:

2-pentene-1,5-dioic acid dihydrazide Maleic acid dihydrazide a,a'-dimethylmuconic acid dihydrazide a-methylmuconic acid dihydrazide B-methylmuconic acid dihydrazide a,fl'-dimethylmuconic acid dihydrazide a,a',B-trimethylmyconic acid dihydrazide a,B,,B-trimethylmuconic acid dihydrazide a,a,B,B'-tetramethylmuconic acid dihydrazide 2,4,6,8-decatetraenel lO-dioic acid dihydrazide 3,4-diisopropyl-2,4-hexadiene-1,6-dioic dihydrazide 2,6,1 1,15-tetramethyl-2,6,10,14-hexadecatetraene 1,20-dioic acid-hydrazide 9-heneicosene-1,21dioic acid dihydrazide 2,6,l0,15,l9,23-hexamethyl-2,6,10,14,l8,22-

tetracosahexene-l ,24-dioic acid dihydrazide Z-tetratriacontenel ,34-dioic acid dihydrazide 2,6,l0,l4,l9,23,27,3l-octamethyl- 2,6,l0,14,l8,22,26,30-dotriacontaoctaene acid dihydrazide Each of the above disclosed mono and dihydrazide compounds are effective auxiliary accelerators for vulcanizing ethylene-propylene-diene elastomer compositions.

Another class of hydrazide compounds suitable for use as auxiliary accelerators in vulcanizing EPDM elastomeric compositions can be defined by the structural formula acid dioic wherein Y can be or hydrogen and R is a C to C divalent aryl hydrocarbon radical. in the instance wherein Y is hydrogen, monohydrazide compounds suitable for use in the methods and compositions of the present invention can include:

Benzoic acid hydrazide 3,4-dimethyl benzoic acid hydrazide 3,4,5-trimethyl benzoic acid hydrazide 2,3,4,5,6-pentamethylbenzoic acid hydrazide 9-phenyl antracene- 1 O-carboxylic hydrazide l-(4-biphenyl)-4-naphthoic acid hydrazide l-(4-benzoic acid hydrazide)-tricosane l-(4-benzoic acid hydrazide) heptacosane l-(4-benzoic acid hydrazide) tritriacontane Compounds in which Y is and R is a C to C divalent aryl hydrocarbon radical, compounds suitable for use can include:

Terephthalic acid dihydrazide 5-methyl isophthalic acid dihydrazide 4,6-dimethyl isophthalic acid dihydrazide 2,6-naphthalene dicarboxylic acid dihydrazide l, l -binaphthyl-4,4'-dicarboxylic acid dihydrazide Benzo (c) phenanthrene-3,l l-dicarboxylic acid dihydrazide Picene-1,7-dicarboxylic acid dihydrazide l,l-(p-benzoic acid hydrazide) hexadecane p-terephenyl-4,4'-dibenzoic acid hydrazide l,l-( p-benzoic acid hydrazide) hexacosane The above disclosed aryl acid hydrazide compounds are effective as auxiliary accelerators in the sulfur vulcanization of EPDM synthetic elastomeric compositions when added thereto.

As one illustration of the methods and compositions of the present invention, the following example is herein presented. All parts and percentages unless otherwise stated are by weight. The following EPDM sulfur vulcanizable compositions of NORDEL 1070, an ethylene-propylene-diene polymer commercially available, were prepared.

Parts by weight A B C D E F G H Nordel 1070 100 100 100 100 100 100 100 100 Zinc oxide 5.0 5.0 5.0 5. 5. 0 5. 0 5. 0 5. 0 HAF carbon black" 50. 0 50. 0 50.0 50. 0 50.0 50. 0 50. 0 50. (l 'IM'IDS 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1. Rubber cxtendln oil (ASTM D-2226 0. 0 20. 9 20. 9 20. 0 20. 9 20. 0 20. 0 20. 0 MBT 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Suliur 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Acethydrazlde 0. 2 Bcnzolc acid hydrazide 0. 2 Adi ic acid dihydrnxidr 0. 2 Pht ulic acid dihydrazide 0. 2 a,u'-Dlmcthylmucouic acid dihydrazide 0. 2 2,6-dicarboxylic naphthalene di tydruzidc... 0. MDT 9 .2

l Tetramethglthiuram disulilde. 9 Z-Mercapto cnzothiszole.

Time to Optimum Tensil 300% elonghard- Example Cure psi modulus ation ness A-Control 22 min. 2750 1400 450 62 B-Acethydruzidc 16 min. 2700 i425 385 61 C-Bcnzoic Acid Hydrazide l5 min. 2725 i375 405 6| D-Adipic Acid Hydrazide l6 min. 2075 I400 390 60 l7 min. i425 440 6i 19 min. 2750 1365 450 60 i8 min. 21 min.

Each of the above EPDM elastomer compositions were cured on a Monsanto Rheometer until the Mooney Viscosity reached a maximum tensil strength of about 2700 psi. The table above lists the length of time required for each of the compounds to reach this optimum cure at 320 F. The control as can be recognized required 23 minutes of curing time in order to achieve the maximum cure. With addition of 0.2 parts MBT as shown in Example G, the cure time wax only shortened by 1 minute. However, the addition of 0.2 parts of the auxiliary accelerators of the compositions of the present invention substantially improved and lessened the time necessary for an EPDM elastomer of the type herein disclosed to reach maximum cure. A substantial improvement in the vulcanization of EPDM elastomers by the hydrazides of the mono and dibasic acids as herein disclosed is clearly demonstrated.

The EPDM compositions of the present invention can also include the other additives normally used in the preparation of rubber products from EPDM polymers. Fillers and extenders normally used are considered within the scope of the present invention. Fillers such as carbon black, oxides of metals, talcums, clay, calcium carbonate, among others, can be used within the compositions of the present invention. Extenders such as petroleum hydrocarbon oils of the kind generally classified in ASTM D-2226 are suitable for use in the compositions of the present invention.

The scope of the present invention is not limited to the specific examples herein above presented. Any of the well known ethylene-propylene-diene elastomers generally used and available in the art when combined with any of the herein above disclosed mono and dihydrazides of monobasic and dibasic organic acid provide substantially improved sulfur vulcanizable EPDM elastomer compositions.

The invention claimed is:

l. A improved sulfur vulcanizable ethylenepropylene-diene polymer composition having a substantially accelerated cure-rate consisting essentially of ethylene-propylene-diene polymer, sulfur and a vulcanization improving quantity of an auxiliary accelerator selected from the group of compounds having a structural formula wherein R is selected from the group consisting of C 1 to C aryl, alkyl, alkenyl and cyclic divalent hydrocarbon radicals or O R-iiI-NHNH:

4. A composition according to claim 1 wherein R is aliphatic.

5. A composition according to claim 4 wherein the the vulcanization improving compound is acethydrazide.

6. A composition according to claim 1 wherein R is aromatic.

7. A composition according to claim 6 wherein the vulcanization improving compound is the hydrazide of benzoic acid.

8. A composition according to claim 1 wherein the polymer is ethylene-propylene-l ,4-hexadiene.

9. In the process of vulcanizing sulfur-vulcanizable ethylene-propylene-diene polymer which comprises mixing ethylene-propylene-diene polymer with a sulfur containing vulcanizing agent, the improvement which comprises improving the cure-rate of the composition by adding to the composition prior to heating a vulcanization improving quantity of an auxiliary accelerator selected from the group of compounds having a structural formula o 0 11NHNbR(":NHNH1 wherein R is selected from the group consisting of C to C aryl, alkyl, alkenyl and cyclic divalent hydrocarbon radicals or o R-llNHNHz wherein R is selected from the group consisting of C to C aryl, alkyl, alkenyl and cyclic monovalent hydrocarbon radicals.

10. A method according to claim 9 wherein in polymer is ethylene-propylene-l ,4-hexadiene.

11. A process according to claim 9 wherein the auxiliary accelerator is acethydrazide.

12. A process according to claim 9 wherein the auxiliary accelerator is benzoic acid hydrazide.

13. A process according to claim 9 wherein the auxiliary accelerator is adipic acid dihydrazide.

14. A process according to claim 9 wherein the auxiliary accelerator is phthalic acid dihydrazide. 

2. A composition according to claim 1 wherein the vulcanization improving compound is the dihydrazide of succinic acid.
 3. A composition according to claim 1 wherein the vulcanization improving compound is the dihydrazide of adipic acid.
 4. A composition according to claim 1 wherein R is aliphatic.
 5. A composition according to claim 4 wherein the the vulcanization improving compound is acethydrazide.
 6. A composition according to claim 1 wherein R is aromatic.
 7. A composition according to claim 6 wherein the vulcanization improving compound is the hydrazide of benzoic acid.
 8. A composition according to claim 1 wherein the polymer is ethylene-propylene-1,4-hexadiene.
 9. In the process of vulcanizing sulfur-vulcanizable ethylene-propylene-diene polymer which comprises mixing ethylene-propylene-diene polymer with a sulfur containing vulcanizing agent, the improvement which comprises improving the cure-rate of the composition by adding to the composition prior to heating a vulcanization improving quantity of an auxiliary accelerator selected from the group of compounds having a structural formula wherein R is selected from the group consisting of C1 to C40 aryl, alkyl, alkenyl and cyclic divalent hydrocarbon radicals or wherein R is selected from the group consisting of C1 to C40 aryl, alkyl, alkenyl and cyclic monovalent hydrocarbon radicals.
 10. A method according to claim 9 wherein in polymer is ethylene-propylene-1,4-hexadiene.
 11. A process according to claim 9 wherein the auxiliary accelerator is acethydrazide.
 12. A process according to claim 9 wherein the auxiliary accelerator is benzoic acid hydrazide.
 13. A process according to claim 9 wherein the auxiliary accelerator is adipic acid dihydrazide.
 14. A process according to claim 9 wherein the auxiliary accelerator is phthalic acid dihydrazide. 